Unexpected high production of biohydrogen from the endogenous fermentation of grape must deposits

The aim of this work was to assess the performances of wine byproduct biomass for hydrogen production by dark fermentation. Grape must deposits from two grape varieties (Pinot Gris and Chardonnay) were considered, either with external microbial inoculum or without. We show that grape must residues contain endogenous microflora, well adapted to their environment, which can degrade sugars (initially contained in the biomass) to hydrogen without any nutrient addition. Indeed, hydrogen production during endogenous fermentation is as efficient as with an external heat-treated inoculum (2.5 +/- 0.4 L-H2.L-reactor(-1) and 1.61 +/- 0.41 mol(H2).mol(consumed hexose)(-1), respectively) with a lower energy cost. Hydrogen-producing bacteria were selected from the endogenous microflora during semi-batch bioreactor operation, as shown by T-RFLP profiles and 16S rRNA sequencing, with Clostridium spp. (butyricum, beijerinckii, diolis, roseum) identified as the major phylotype. Such hydrogen production efficiency opens new perspectives for innovating in the valorization of winery by-products.

Automated summary

The study found that endogenous microflora in grape must residues can degrade sugars in the biomass to produce hydrogen without any nutrient addition, with similar efficiency to external microbial inoculum. Clostridium spp. were identified as the major hydrogen-producing bacteria, offering new possibilities for utilizing winery by-products.